Apparatus for controlling pressure in a cylinder chamber of a hydraulic pump-motor

ABSTRACT

An apparatus controls a pressure in a cylinder chamber of a hydraulic pump-motor. The cylinder chamber is formed by fitting a piston in a cylinder bore of a rotatable cylinder block, and the cylinder block is rotated so that ports going to the cylinder chambers are alternatively opened to a high pressure port and a lower pressure port that are both formed in a valve plate. The apparatus includes a first switching port formed at a top dead point side of the valve plate, the first switching port being communicated with a tank through a first open-close valve. A second switching port is formed at a bottom dead point of the valve plate, the second switching port being communicated with the high pressure port through a second open-close valve. A rotational speed detector detects a rotational speed of the cylinder block, a pressure detector detects a maximum pressure in the cylinder chamber and a control device controls opening and closing timings and opening magnitude of the first and second open-close valves in response to the rotational speed and the maximum pressure.

TECHNICAL FIELD

The present invention relates to an apparatus for controlling pressurein a cylinder chamber of a hydraulic pump-motor.

BACKGROUND ART

As shown in FIG. 1, there is known a piston-type hydraulic pump-motor inwhich a cylinder block 3 secured to a shaft 2 is disposed inside acasing 1 to be rotatable, plurality of cylinder chambers 6 are formedinto which pistons 5 are respectively fitted in a plurality of cylinderbores 4 of the cylinder block 3. The respective pistons 5 are disposedto be slidable in respective axial directions thereof in accordance withthe rotation of the cylinder block 3 through slidable abutment of outerend portions of the pistons 5 against a swash plate 8 through pistonshoes 7. And as shown in FIG. 2, the cylinder chambers 6 arecommunicated with high and low pressure ports 10 and 11 formed in avalve plate 9 so as to alternately at every 180° rotation.

In such a hydraulic pump-motor, as shown in FIG. 2, ports 12 open to thecylinder chambers 6 alternately communicated with the high pressureports 10 and the low pressure port 11 at top and bottom dead points ofthe valve plate 9 to thereby switch the operation "from drain tosuction" and "from suction to drain".

Fine grooves 10a and 11a are formed with the high and low pressure ports10 and 11 so as not to cause a rapid pressure change at the time of thisswitching operation.

That is, if the port 12 is suddenly communicated with the high or lowpressure port 10 or 11, the pressure in the cylinder chamber 6 rapidlychanges, thus causing hydraulic pressure pulsation or large noise. Inorder to prevent the pressure in the cylinder chamber 6 from rapidlychanging, the fine grooves 10a and 11a are formed with the high and lowpressure ports 10 and 11 so that the ports 12 are gradually open theretothrough the fine grooves 10a and 11a.

However, since the shapes and sizes of the fine grooves 10a and 11a aremade constant and the valve plate 9 is not moved, the port 12 alwaysassumes a constant open position. Accordingly, it is difficult to alwaysachieve most suitable operational characteristics at the time ofchanging the rotating speed of the cylinder block 3 or the maximumpressure in the cylinder chamber 6 at which the hydraulic pressurepulsation or noise will be caused.

SUMMARY OF THE INVENTION

The present invention aims to provide an apparatus for controllingpressure in a cylinder chamber of a hydraulic pump-motor that is capableof solving the problems described above.

Thus, an object of the present invention is to provide an apparatus forcontrolling pressure in a cylinder chamber that is capable of alwaysachieving the most suitable operational characteristics by opening orclosing switching ports in response to a rotational speed or a maximumpressure in a cylinder chamber to thereby prevent the pressure in thecylinder chamber from rapidly changing, thus preventing hydraulicpressure pulsation and noise from being caused.

The apparatus for controlling a pressure in the cylinder chamberaccording to the present invention was conceived in consideration of theabove matters, and in order to achieve the above and other objects,there is provided, in one aspect, an apparatus for controlling apressure in a cylinder chamber of a hydraulic pump-motor in which acylinder chamber is formed by fitting a piston in a cylinder bore thatis formed to in a rotatable cylinder block. The cylinder block isrotated so that ports to the cylinder chambers are alternately opened toa high pressure port and a low pressure port, both parts being formed ina valve plate. The apparatus being has a first switching port formed ata top dead point side of the valve plate. The first switching port beingis communicated with a tank through a first open-close valve. A secondswitching port is formed at a bottom dead point of the valve plate, andthe second switching port is communicated with the high pressure portthrough a second open-close valve and comprises a rotational speeddetection means for detecting a rotational speed of the cylinder block,a pressure detection means for detecting a maximum pressure in thecylinder chamber and a control means for respectively controlling theopening and closing timings and opening magnitude of the first andsecond open-close valves in response to the rotational speed and themaximum pressure.

According to this structure, since the opening and closing timings ofthe first and second open-close valves can be controlled in response tothe rotational speed of the cylinder block and the opening magnitude ofthe first and second open-close valves can be also controlled by themaximum pressure in the cylinder chamber, the opening and closingtimings of the first and second switching ports, the drain amount fromthe cylinder chamber and the supply amount to the cylinder chamber canbe controlled. Thus the most suitable operational characteristics canalways be achieved, preventing the pressure in the cylinder chamber fromrapidly changing and hence reducing the hydraulic pressure pulsation andnoise.

In a preferred example, the first and second open-close valves areopened or closed by electrostrictive elements, the rotational speeddetection means is a rotation speed sensor, the pressure detection meansis a pressure detection sensor, and the control means is a controllerfor controlling current conduction to the electrostrictive elements inresponse to the maximum pressure in the cylinder chamber detected by thepressure detection sensor and controlling current conduction timings tothe electrostrictive elements in response to the rotational speed of thecylinder block detected by the rotation speed sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be made more understandable through thefollowing detailed disclosure and the accompanying drawings representingan embodiment of the present invention. Further, it is to be noted thatthe embodiment illustrated in the drawings does not specify the presentinvention and is for easy explanation and understanding of theinvention.

FIG. 1 is a schematic sectional view of a hydraulic pump-motor.

FIG. 2 is a front view of a valve plate of the hydraulic pump-motor ofFIG. 1.

FIG. 3 is a view showing a structure of one embodiment of an apparatusfor controlling a pressure in a cylinder chamber of a hydraulicpump-motor according to the present invention.

FIG. 4 is a partial enlarged view showing a switching port of theabove-described embodiment of FIG. 3.

FIG. 5 is a control circuit diagram of the above-described embodiment ofFIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereunder, an apparatus for controlling a pressure in a cylinder chamberof a hydraulic pump-motor according to one preferred embodiment of thepresent invention will be described with reference to FIGS. 3 to 5.

As shown in FIG. 3, first and second switching ports 20 and 21 areformed in a valve plate 9 on the top and bottom dead point sides,respectively. The first and second switching ports 20 and 21 each has adiameter smaller than the distance between ports 12 and 12 that go tocylinder chambers 6, as shown in FIG. 4.

The first switching port 20 is communicated with a tank 23 through afirst open-close valve 22 and the second switching port 21 iscommunicated with a high pressure port 10 through a second open-closevalve 24.

The first and second open-close valves 22 and 24 are each of anelectromagnetic open-close type structure in which a valve 25 is held atits closed position by means of a spring 26 and is pushed to its openedposition by means of an electrostrictive element 27. According to thisstructure, a large thrust force and a high degree of responsiveness canbe achieved by using the electrostrictive element 27, and the openingarea of the valve can be increased or decreased in response to amount ofelectrical current conduction to the electrostrictive element 27.

The electrical current conduction to each of the electrostrictiveelements 27 is controlled by a controller 28 as shown in FIG. 5. To thecontroller 28, drain pressure detected by a pressure sensor 29, that is,the maximum pressure in the cylinder chamber 6, is inputted, and therotational speed of an engine 31 detected by a rotation sensor 30, thatis, the rotational speed of a hydraulic pump 32, is also inputted.

The embodiment of the structure described above will operate in thefollowing manner.

During the movement of the port 12 to the side of the low pressure port11 from the side of the high pressure port 10, when the port 12 reachesthe first switching port 20, a current is conducted to theelectrostrictive element 27 of the first open-close valve 22 to therebyopen the valve 25 and hence to drain a highly pressurized oil in thecylinder chamber 6 to the tank 23. In this operation, the opening areaof the first open-close valve 22 can be increased or decreased bycontrolling the electrical conduction amount to the electrostrictiveelement 27, thereby controlling the drain amount from the cylinderchamber 6.

Similarly, during the movement of the port 12 to the side of the highpressure port 10 from the side of the low pressure port 11, when theport 12 reaches the second switching port 21, a current is conducted tothe electrostrictive element 27 of the second open-close valve 24thereby to open the valve 25 and hence to supply a highly pressurizedoil in the high pressure port 10 to the cylinder chamber 6. In thisoperation, the opening area of the second open-close valve 24 can beincreased or decreased by controlling the electrical conduction amountto the electrostrictive element 27, thereby controlling the supplyamount to the cylinder chamber 6.

Accordingly, the most suitable operational characteristics can always beachieved, even if the rotational speed of the cylinder block and themaximum pressure in the cylinder chamber 6 are changed, by controllingthe electrical conduction timing to the electrostrictive elements 27 ofthe first and second open-close valves 22 and 24 via the rotationalspeed from the rotation sensor 30 and controlling the electricalconduction amount to the electrostrictive elements 27 via the pressurefrom the pressure sensor 29.

As described above, according to the present invention, the timing foropening or closing the first and second open-close valves 22 and 24 canbe controlled by the rotational speed of the cylinder block and theopening degrees of the first and second open-close valves 22 and 24 canbe also controlled by the maximum pressure in the cylinder chamber, sothat the most suitable operational characteristics can be achieved fromthe first and second switching ports 20 and 21 in response to therotational speed of the cylinder block and the maximum pressure in thecylinder chamber, thereby preventing the pressure in the cylinderchamber from rapidly changing and hence reducing the hydraulic pressurepulsation and noise from causing.

As described above, the apparatus for controlling the pressure in thecylinder chamber of the hydraulic pump-motor is extremely useful as anapparatus for controlling various types of hydraulic pump-motors.

Further, it is a self-evident to those skilled in the art that althoughthe present invention has been described with reference to the exemplaryembodiment, other various changes, deletions and additions can be madewithout departing from the subject and scope of the present inventionwith respect to the described embodiment. Accordingly, it is to beunderstood that the present invention is not limited to the describedembodiment, and includes the scope prescribed by the elements recited inthe claims and equivalents thereof.

I claim:
 1. An apparatus for controlling pressure in a cylinder chamber of a hydraulic pump-motor, the hydraulic pump-motor comprising a rotatable cylinder block having a bore therein defining a cylinder chamber, a piston in the bore, a port communicating with the cylinder chamber and a valve plate having a high pressure port and a low pressure port, whereby the port communicating with the cylinder chamber is alternately opened to the high pressure port and the low pressure port upon rotation of the cylinder block, said apparatus comprising:a first switching port formed at a top dead point side of the valve plate; a tank communicating with said first switching port through a first open-close valve; a second switching port formed at a bottom dead point side of the valve plate communicating with the high pressure port through a second open-close valve; a rotational speed detecting means for detecting the rotational speed of the cylinder block; a pressure detection means for detecting a maximum pressure in the cylinder chamber; and a control means for controlling timing of the opening and closing and opening magnitude of said first and second open-close valves in response to the rotational speed and the maximum pressure detected by said rotational speed detecting means and said pressure detection means.
 2. The apparatus of claim 1, wherein:said first and second open-close valves each comprises a valve element and an electrostrictive element for opening and closing said valve element; said rotational speed detection means comprises a rotation speed sensor; said pressure detection means comprises a pressure detection sensor; and said control means comprises a controller that controls current conduction to said electrostrictive elements in response to the maximum pressure in the cylinder chamber detected by said pressure detection sensor and controls the timing of current conduction to said electrostrictive elements in response to the rotational speed of the cylinder block detected by said rotation sensor.
 3. An apparatus, comprising:a hydraulic pump-motor comprising a rotatable cylinder block having a bore therein defining a cylinder chamber, a piston in the bore, a port communicating with said cylinder chamber and a valve plate having a high pressure port, a low pressure port, a top dead point side and a bottom dead point side, whereby said port communicating with said cylinder chamber is alternately opened to said high pressure port and said low pressure port upon rotation of said cylinder block; a first switching port formed at said top dead point side of said valve plate; a tank communicating with said first switching port through a first open-close valve; a second switching port formed at said bottom dead point side of said valve plate communicating with the high pressure port through a second open-close valve; a rotational speed detecting means for detecting the rotational speed of said cylinder block; a pressure detection means for detecting a maximum pressure in said cylinder chamber; and a control means for controlling timing of the opening and closing and opening magnitude of said first and second open-close valves in response to the rotational speed and the maximum pressure detected by said rotational speed detecting means and said pressure detection means.
 4. The apparatus of claim 3, wherein:said first and second open-close valves each comprises a valve element and an electrostrictive element for opening and closing said valve element; said rotational speed detection means comprises a rotation speed sensor; said pressure detection means comprises a pressure detection sensor; and said control means comprises a controller that controls current conduction to said electrostrictive elements in response to the maximum pressure in the cylinder chamber detected by said pressure detection sensor and controls the timing of current conduction to said electrostrictive elements in response to the rotational speed of the cylinder block detected by said rotation sensor. 